In a conventional practice, elastomer latex is coagulated to form raw rubber in the form of small crumbs of about 3 to 5 millimeters particle size, which are then filtered, washed to remove soap, and dried. Raw rubber is a tacky material which agglomerates readily into large chunks or bales. Anticaking agents have been admixed in the past with raw crumb rubber to maintain it in particulate form, however, even these agents are not effective in maintaining raw rubber in free-flowing state and they may be detrimental to the inherent properties of rubber.
In commercial practice, raw rubber is usually delivered in large chunks or bales which may be subdivided by cutting into smaller pieces which are subsequently processed in a conventional manner by mixing with other ingredients. Since such mixing is an energy intensive procedure, the use of powdered, friable rubber would substantially reduce energy requirements.
The prior art has dealt with the problem of rendering the raw rubber in a free-flowing powdered form. U.S. Pat. No. 3,813,259 to Neubert, in a preferred embodiment, discloses a process for obtaining dry, non-adhering particles by adding styrene-butadiene latex to a coagulant solution whereby the latex is coagulated to produce raw rubber in the form of crumbs. This process is completed by heating the resulting mixture to an elevated temperature, adding a coating resin latex to the heated mixture in order to deposit a layer of the coating resin on the particles of raw rubber, and recovering an allegedly nonagglomerating particulate product with a particle diameter on the order of one quarter of an inch.
Japanese Pat. Nos. 54(1979)-7448 and 7449 relate to a process for preparing powdered polychloroprene rubber. This is accomplished by admixing methylcellulose, hydroxymethyl cellulose or polymethyl vinyl ether with polychloroprene latex and a sulfate or a carbonate of an alkali metal. This mixture is maintained at room temperature or heated to above 50.degree. C. and added dropwise with stirring to a coagulant solution of an alkaline earth chloride or nitrate maintained at a temperature from about 30.degree. C. to above 50.degree. C. A coating resin latex is added to the coagulant with mixing for about one hour following which, the mixture is filtered, the filter cake is washed with dilute acid and then with water, and dehydrated with a centrifuge to obtain a fluid powdery rubber which is easily pulverizable. The product, for the most part, allegedly consists of particles smaller than 14 mesh or 3 millimeters.